This invention relates to a design and method of fabrication of a collapsible, flexible storage tank; and in particular, to a flexible storage tank of the pillow tank variety that includes seams that are formed in a spiral configuration about the pillow tank.
It is often desirable to have a container storage tank capable of holding a liquid such that when there is no liquid in the container, it may be collapsed or folded for ease of transportation and storage. Collapsible liquid containers have been available for some time and encompass a variety of designs. One example of an early collapsible container of the pillow tank variety is found in U.S. Pat. No. 2,724,418 to Krupp, which is incorporated in its entirety herein by reference. Krupp discloses a flexible container that includes a volume responsive pressure relief valve and overflow valve assembly. In addition, the tank in Krupp includes a connector fitting, an attachable cap fitting for filling a drain in a tank. The tank also includes attached flexible handles. The containers are made from a flexible sheet material having an intermediate layer or a plurality thereof of square-woven textile fabric sheet material of cotton, nylon, rayon, glass fibers or other suitable filamentary material having the desired strength characteristics. The material is coated or treated with a suitable natural or synthetic rubber composition. The material may also include an outer protective layer of suitable rubber composition having age resisting and abrasion resisting characteristics, an inner layer of gasoline resistant rubber compositions, such as, for example, a copolymer of butadiene and acrylonitrile or a neoprene. The container is assembled by joining and adhering in a suitable known manner, including a plurality of pre-cut patterns of suitable flexible sheet material. The materials are joined in laterally extending seams of overlapped, fabric tape reinforced construction.
Another form of flexible container is found in U.S. Pat. No. 3,510,142 to Erke, which is incorporated in its entirety herein by reference. Erke discloses a portable, collapsible tank having an inflatable double walled construction with tie down means secured thereto. The tank in Erke has a double walled inflatable structure with one or more fill/drain ports. The tank is designed to receive and retain a variety of liquids or dry powder materials.
Another pillow tank is disclosed in U.S. Pat. No. 4,865,096 to Schober et al., which is incorporated in its entirety herein by reference. Schober et al. discloses a pillow tank with upper and lower sections, which are secured together along a seam extending around the mid section of the tank. A sleeve extends along a mid line of the entire perimeter of the seam. Slits or holes are formed through the sleeve to permit a rope to be threaded through portions of the sleeve to form tie-down points for the tank. The tank may also include exterior strapping in different configurations that can be sewn or secured to the tank for added strength. The tank is formed of a tube defined by an upper rectangular section and a lower rectangular section bonded together. Material for the tank may be typical elastomeric coated cloth panels, which may be square woven nylon cloth with a coating of neoprene or SBR rubber. Typical nylon cloth weights in a tank would be 5 and 13 ounces per square yard, although other weave patterns of nylon cloth can be used. Elastic coated aramid fibers may also be suitable material for manufacturing the tank.
Another flexible container is disclosed in U.S. Pat. No. 4,875,596 to Lohse, which is incorporated in its entirety herein by reference. The vessel in Lohse is designed for transporting or storing bulk materials or liquids and is shaped in the form of a tube having open ends tightly sealed by means of a straight line clamp or connection parts. The clamp connection parts are formed toothed rack-like so that, with relatively short clamp connections, tubes with relatively large openings can be sealed tightly.
U.S. Pat. No. 6,186,713 B1 to Bonerb discloses a bulk liquid freight transport vehicle, which is incorporated in its entirety herein by reference. The transport includes a collapsible liquid cargo bag and at least one adjustable cinching strap for being tightened down over the bag. Tightening of the strap over the bag causes the pressure of the liquid mass within the bag to increase to prevent motion of the liquid in the bag through motion of the vehicle.
A different type of flexible storage tank is disclosed in U.S. Pat. No. 6,842,955 B2 to Joshi et al., which is incorporated in its entirety herein by reference. The tank disclosed by Joshi et al. has a frusto-conical sidewall configuration and an open top. The tank is constructed of a material such as DuPont Elvaloy™, which is an ethylene-based polymer with reinforced synthetic fibers. Sections of the tank are joined using a heat sealing technique, such as radio frequency welding, ultrasonic heating, heating with hot air, electrical resistant heat, or other methods.
U.S. Patent Application Publication No. US 2009/0001085 A1 to Bartz et al. discloses a flexible tank, which is incorporated in its entirety herein by reference. The tank in Bartz et al. includes an internal baffle apparatus comprising a plurality of panel members connected along a connection line that defines an axis. Panel members extend in a diagonal fashion towards corners of the tank and also extending vertically between the top and bottom of the tank.
U.S. Pat. No. 7,717,296 B1 to Guthrie discloses a transportable and collapsible fabric tank with an integral balloon baffle system, which is incorporated in its entirety herein by reference. The tank in Guthrie is made from a fabric-composite-based material impregnated with polytetrafluoroethylene (PTFE). The internal baffles aid in the stability of the tank to prevent sloshing of the liquid while traveling with the tank partially filled. Internal baffles inflate to sizes large enough to force liquids out of the tank through the discharge valve.
Typical in this construction of prior art tanks, and especially large tanks, is the use of rectangular-shaped sheets that are sealed together along seams. This typically results in seams running longitudinally or laterally across the bottom and top of the tank. In addition, closing seams are also typically located along the side ends. In the longitudinal and lateral seams, there is typically a double thickness of material, where the material from adjacent sheets is overlapped and sealed together. In the side end seams, or closing seams of the tank, there is a triple or three-layer thickness in the area where the longitudinal seams meet the side end seams. Because of the problems in trying to properly seal this three-layered seam area, this is a potential leak path for flexible pillow tanks.
Accordingly, it is an object of the subject invention to reduce or minimize the number of seams, and in particular to eliminate or reduce the number of overlapping seams of triple thickness in material where longitudinal seams meet closing seams.
Another problem with prior art pillow tanks is that the lap joints that are standard for the longitudinal and latitudinal seams may present a leak path. In particular, if the interior lining layer is either damaged or degraded over time or through a lap end, the liquid, especially a corrosive liquid, such as fuel, may enter the middle fabric reinforced layer of the tank's wall and dissolve and propagate creating a leak path. This can be especially problematic in the area of a lap joint. Accordingly, it is another object of the present invention to provide butt joints/seams that are less susceptible to creating and/or providing a leak path for liquid contained in the tank than standard lap seams.